all my " GOOD" listings have a 0% NCX,(negative customer experience)- beyond me how any could get to be an “EXCELLENT” ??

As you correctly highlighted: NCX is “Negative Customer Experience”.
This doesn’t tell you how much positive customer experience items have had.
I would presume items with a high positive rating get excellent status.

Paul73:

Poor means that the item is at risk of being removed.

Usually the listing isn’t “removed” per-se, it is temporarily closed to give you chance to fix potential problems and re-list. It will only get closed in a slightly more permanent way if the problems persist after this has happened once or twice already, in this case you then have to open a case with seller support to have it re-listed.
There’s only two exceptions to this I’m aware of:
When the FBA team has deemed the packaging to be a severe and unresolvable problem, such as sending garden gnomes into FBA in poly bags without bubble wrap (yes… this happened).
The other is when the customer complaints relate to receiving the wrong item from FBA, the FBA team has checked and found the items in your inventory do not match the listing.